03: Perfectly Spherical Houses in a Vacuum

library(tidyverse)

── Attaching packages ─────────────────────────────────────── tidyverse 1.3.2 ──
✔ ggplot2 3.4.0      ✔ purrr   0.3.5 
✔ tibble  3.1.8      ✔ dplyr   1.0.10
✔ tidyr   1.2.1      ✔ stringr 1.4.1 
✔ readr   2.1.3      ✔ forcats 0.5.2 
── Conflicts ────────────────────────────────────────── tidyverse_conflicts() ──
✖ dplyr::filter() masks stats::filter()
✖ dplyr::lag()    masks stats::lag()

library(stringr)

dt <- readLines("input.txt")

Warning in readLines("input.txt"): incomplete final line found on 'input.txt'

Part 1

dirX <- function(x) {
  case_when(
    x == "^" ~ 0,
    x == ">" ~ 1,
    x == "<" ~ -1,
    x == "v" ~ 0
  )
}
dirY <- function(x) {
  case_when(
    x == "^" ~ 1,
    x == ">" ~ 0,
    x == "<" ~ 0,
    x == "v" ~ -1
  )
}

df <- data.frame("x" = 0, "y" = 0)
for(i in 1:nchar(dt))
  df <- rbind(df, data.frame("x" = dirX(substr(dt, i, i)),
                             "y" = dirY(substr(dt, i, i))))
df <- data.table::data.table(df)
df$cumX <- cumsum(df$x)
df$cumY <- cumsum(df$y)
df <- df[, .(cumX, cumY)]
nrow(unique(df))

[1] 2565

Part 2

dfR <- data.frame("x" = 0, "y" = 0)
dfS <- data.frame("x" = 0, "y" = 0)
for(i in seq(1, nchar(dt), 2))
  dfS <- rbind(dfS, data.frame("x" = dirX(substr(dt, i, i)),
                               "y" = dirY(substr(dt, i, i))))
for(i in seq(2, nchar(dt), 2))
  dfR <- rbind(dfR, data.frame("x" = dirX(substr(dt, i, i)),
                               "y" = dirY(substr(dt, i, i))))

dts <- data.table::data.table(dfS)
dts$cumX <- cumsum(dts$x)
dts$cumY <- cumsum(dts$y)
dtr <- data.table::data.table(dfR)
dtr$cumX <- cumsum(dtr$x)
dtr$cumY <- cumsum(dtr$y)

df <- data.table::data.table(rbind(dts, dtr))

df <- df[, .(cumX, cumY)]
nrow(unique(df))

[1] 2639